Buffer, Hydrion(R), TriChek, Chemenvelope Set - The Hydrion Tri-Chek Buffer Chemvelope Calibration Set is perfect for quick and easy pH meter calibration. When mixed with distilled or de-ionized water, Hydrion Buffer Chemvelopes will accurately produce 500 ml of solution at pH 4.00, 7.00 and 10.00. Hydrion Buffers are free flowing soluble powders that prepare clear or color safe solutions in minutes. The set contains three Chemvelopes at pH 4.00, four Chemvelopes at pH 7.00 and three Chemvelopes at pH 10.00. Each Chemvelope produces 500 ml of solution. Included with the set is 1 vial of Hydrion Color Key Buffer Preservative which prolongs the shelf life of the solution and automatically tints each solution to its own color value: orange for ph 4.00, green for ph 7.0 and blue for ph 10.0.